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Cited by 631Memory Processes and InfluencesVisual and Cognitive Learning ProcessesMemory and Neural Mechanisms

Spacing Effects in Learning: A Temporal Ridgeline of Optimal Retention

Open access
Cepeda, Nicholas J., Vul, Edward, Rohrer, Doug, Wixted, John T., Pashler, Harold·2008·Psychological Science
DOI 10.1111/j.1467-9280.2008.02209.x
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Abstract

To achieve enduring retention, people must usually study information on multiple occasions. How does the timing of study events affect retention? Prior research has examined this issue only in a spotty fashion, usually with very short time intervals. In a study aimed at characterizing spacing effects over significant durations, more than 1,350 individuals were taught a set of facts and--after a gap of up to 3.5 months--given a review. A final test was administered at a further delay of up to 1 year. At any given test delay, an increase in the interstudy gap at first increased, and then gradually reduced, final test performance. The optimal gap increased as test delay increased. However, when measured as a proportion of test delay, the optimal gap declined from about 20 to 40% of a 1-week test delay to about 5 to 10% of a 1-year test delay. The interaction of gap and test delay implies that many educational practices are highly inefficient.

Integrity signals

Registry

Crossref · 10.1111/j.1467-9280.2008.02209.x

Cites

32 of 32 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

3 of 24 cited sources checked · 2 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    Several studies involving modest time intervals ranging from minutes to days have found that memory at the final test is best for intermediate gap durations.

    “Several studies involving modest time intervals ranging from minutes to days have found that memory at the final test is best for intermediate gap durations (e.g., Balota, Duchek, & Paullin, 1989;Glenberg, 1976;Glenberg & Lehmann, 1980;Young, 1966; see Cepeda et al., 2006, for a meta-analysis focused on this point).”
    Quote in the paperSubstantial claim1 of 3 sources checked
    • cites Balota, Duchek, & Paullin, 1989

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Glenberg, 1976 source
    • cites Cepeda et al., 2006 source
  • Interpretationreasoning

    Encoding variability and study-phase retrieval theories are potentially consistent with the basic results seen in Figure 3.

    “Other distributed practice theories, such as encoding variability (Glenberg, 1979) and study-phase retrieval (Murray, 1983) are potentially consistent with the basic results seen in Figure 3.”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites Glenberg, 1979 source
    • cites Murray, 1983

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Findingown data

    For a fixed amount of study time, the optimal gap provided a 26% increase, d = 1.5, in final recognition as compared to a zero-day gap.

    “For a fixed amount of study time, the optimal gap provided a 64% increase, d = 1.1, in final recall, and a 26% increase, d = 1.5, in final recognition, as compared to a zero-day gap”
    Quote in the paperSubstantial claim
  • Findingown data

    For 7, 35, 70, and 350 day RIs, percentage improvements in recall for optimal versus zero-day gaps were 10, 59, 111, and 77%, respectively.

    “For 7, 35, 70, and 350 day RIs, percentage improvements in recall for optimal versus zeroday gaps were 10, 59, 111, and 77%-t(124) = 6.5, p rep = .99,d = 1.3; t(111) = 8.9, p rep = .99,d = 0.6; t(102) = 8.6, p rep = .99,d = 1.7; t(68) = 3.9, p rep = .99,d = 0.9, respectively.”
    Quote in the paperSubstantial claim
  • Findingown data

    At any given retention interval, increasing the inter-study gap first increased and then gradually reduced final test performance.

    “At any given retention interval, an increase in the inter-study gap at first increased, and then gradually reduced, test performance.”
    • Also stated in: § Results Figure 3 shows the effect of gap on recall and recognition for each of the four different retention intervals, for the subjects who completed all the phases of the study.For each retention interval, final performance always rose initially with increasing gap and then fell as gap was further increased.The effects of gap were very large in magnitude: For a fixed amount of study time, the optimal gap provided a 64% increase, d = 1.1, in final recall, and a 26% increase, d = 1.5, in final recognition, as compared to a zero-day gap (in the present article, d values refer to the comparison of zeroday versus optimal gap).For the RIs of 7, 35, 70, and 350 days, the optimal gaps (of those included in the study) were 1, 11, 21, and 21 days, respectively, for recall data, and 1, 7, 7, and 21 days, respectively, for recognition data.All of these findings are in good agreement with the lab benchmark dataset, which, with its RI of 6 months, lay about where it would be expected to between the RI = 70 and RI = 350 conditionsdespite the fact that the laboratory study fixed session 2 exposure duration and the current study did not.(Both studies provided a fixed number of relearning trials.)For 7, 35, 70, and 350 day RIs, percentage improvements in recall for optimal versus zeroday gaps were 10, 59, 111, and 77%-t(124) = 6.5, p rep = .99,d = 1.3; t(111) = 8.9, p rep = .99,d = 0.6; t(102) = 8.6, p rep = .99,d = 1.7; t(68) = 3.9, p rep = .99,d = 0.9, respectively.For recognition data, percentage improvements for optimal versus zero-day gaps were 1, 10, 31, and 60%-t(124) = 2.3, p rep = .99,d = 0.7; t(136) = 7.5, p rep = .99,d = In Press, Psychological Science Spacing Effects in Learning 5 1.5; t(112) = 8.7, p rep = .99,d = 1.7; t(68) = 7.9, p rep = .99,d = 2.1 for 7, 35, 70, and 350 day RIs, respectively.Estimated optimal gap values rise as retention interval is increased, and these depart noticeably from the fixed ratio of retention interval suggested by some earlier researchers based on much shorter-term studies (Crowder, 1976;Murray, 1983). · boosted
      “For each retention interval, final performance always rose initially with increasing gap and then fell as gap was further increased.”
    Quote in the paperSubstantial claim
  • May combine two claims. 9
  • Classified as probably not a substantial claim. 6
  • The quote only partly states this claim. 1

  • May combine two claims.

    Premisecitation

    Only about a dozen of the more than 400 papers in a recent review of distributed practice studies involving verbal recall looked at retention intervals as long as one day, with just a handful examining retention intervals longer than one week.

    “A recent review of distributed practice studies involving verbal recall (Cepeda et al., 2006) examined more than 400 papers.However, only about a dozen of these looked at retention intervals as long as one day, with just a handful examining retention intervals longer than one week.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Cepeda et al., 2006 source

      Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingown data

    The optimal gap value was about 20% of the test delay for delays of a few weeks, falling to about 5% when the delay was one year.

    “The optimum gap value was about 20% of the test delay for delays of a few weeks, falling to about 5% when delay was one year.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In the fitted function, the optimal gap for RI = 350 equals 23 days, which is just 7% of the RI.

    “In Figure 4, for example, the optimal gap for RI = 350 equals 23 days, which is just 7% of the RI.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Findingreasoning

    For any gap duration, recall performance declines as a function of retention interval in a negatively accelerated fashion.

    “First, for any gap duration, recall performance must decline as a function of RI (i.e., test delay) in a negatively accelerated fashion in order to produce the familiar forgetting curve consistent with more than 100 years of memory findings.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The forgetting curve is negatively accelerated (information loss per unit time gradually shrinks).

  • May combine two claims.

    Findingown data

    The results document the existence of enormous and non-monotonic spacing effects that unfold over very long periods of time, with study time equated across conditions.

    “The results presented here document the existence of enormous and non-monotonic spacing effects that unfold over very long periods of time, with study time equated across conditions.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Findingown data

    Exploration of the data indicated that a number of other functions can also provide quite decent fits to the data, and the presented function is not uniquely accurate.

    “Exploration of the data indicated that a number of other functions can also provide quite decent fits to the data, with various tradeoffs between interpretability of parameters and simplicity of the function, and we do not contend that this function offers a uniquely accurate characterization of the surface-merely a reasonable one.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Each subject was randomly assigned to one of the 26 gap-by-retention interval combinations.

    “There were 26 gap-by-retention interval combinations, and each subject was randomly assigned to one of these.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductown data

    There were no detectable differences between completers and non-completers in age, gender, number of obscure facts known before beginning the study, or a wide array of background and demographic characteristics.

    “There were also no detectable differences between the groups in age, gender, number of obscure facts known before beginning the study, or a wide array of background and demographic characteristics.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    The current study held constant the number of restudy trials in the second study session, allowing the effect of gap to be examined apart from the amount of time provided for restudy.

    “We held constant the number of restudy trials in the second study session, thus allowing us to look at the effect of gap apart from the amount of time provided for restudy.”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Premisecitation

    In Bahrick et al. (1993), increasing the inter-study spacing out to 56 days improved performance in acquisition and retention of foreign language vocabulary over several years.

    “The results showed that increasing the inter-study spacing out to 56 days improved performance (Figure 2).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Bahrick et al., 1993 source

  • May combine two claims.

    Premisecitation

    In a preliminary laboratory-based study (Cepeda et al., 2007), recall success for facts and names was best for a 1-month gap, with much worse recall for shorter gaps and slightly poorer recall for longer ones, when final test was 6 months after second learning session.

    “The non-monotonic pattern noted in short-term studies was indeed found: Recall success (for both facts and names) was best for a 1-month gap, with much worse recall for shorter gaps and slightly poorer recall for longer ones.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Cepeda et al., 2007

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationcitation

    The 56-day gap in Bahrick et al. (1993) was a relatively short proportion of the extremely long retention intervals used, and this ratio is probably most critical.

    “However, 56 days is actually a relatively short proportion of the extremely long retention intervals used in Bahrick et al.'s study, and it is this ratio that is probably most critical, as will emerge below.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Bahrick et al., 1993 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    Non-completion rates increased at the longer delays.

    “Non-completion rates increased at the longer delays, as one would expect in any multi-year study (Table 1)”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    The reliability and validity of internet data collection has become increasingly clear in recent years.

    “As described in the Appendix, the reliability and validity of internet data collection has become increasingly clear in recent years.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Reips, 2002

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Gosling et al., 2004 source

  • May combine two claims.

    Premisecitation

    The validity of internet testing has been well supported in recent reviews, with excellent correspondence between results obtained with internet samples and results obtained in the laboratory.

    “The validity of internet testing has been well supported in recent reviews (Gosling et al., 2004), with excellent correspondence between results obtained with internet samples are results obtained in the laboratory (e.g., Birnbaum, 1999;Krantz & Dalal, 2000;McGraw, Tew, & Williams, 2000;Reips, 2002).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Gosling et al., 2004 source
    • cites Birnbaum, 1999 source
    • cites Reips, 2002

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

15 of 15

  • The paper relies on this without support.

    The 32 obscure trivia facts and object names used in the study are representative of the kinds of information people need to learn and retain in educational settings.

    “Stimuli consisted of 32 obscure but true trivia facts (e.g.,”

  • The paper relies on this without support.

    The forgetting curve is negatively accelerated (information loss per unit time gradually shrinks).

    “The amount of information lost per unit of time gradually shrinks, producing the well-known increasingly gradual forgetting curve.”

  • The paper relies on this without support.

    Working memory operates on a time scale of seconds or minutes.

    “Working memory operates on a time scale of seconds or minutes, whereas gap effects are seen on a scale of day and weeks (optimal gap is several weeks, for longer retention intervals).”

  • The paper relies on this without support.

    The 26 gap-by-retention interval combinations adequately sample the retention surface.

    “To properly characterize the interaction of gap and retention interval, the current study combines various gap and RI values, for a total of 26 different conditions.”
4 of 4

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • The optimal ratio of spacing and retention interval should be 10-30%.

    “The optimal ratio of spacing and retention interval should be 10-30%.”

    From MASSED TASK REPETITION IS A DOUBLE-EDGED SWORD FOR FLUENCY DEVELOPMENT (2022) · cites this paper as Cepeda et al., 2008

    The Discussion (page unavailable) says the ratio of optimal spacing gap to retention interval declines as the retention interval increases; it gives 23 days for a 350-day interval, or 7%. The paper therefore does not recommend a fixed optimal ratio of 10–30% across retention intervals. (LLM, conf=0.90)

    Checked by a reasoning model — may be wrong.

    Experimental — accuracy not yet measured

  • Laboratory research emphasizes that the effect of retention intervals on the distributed practice advantage does not continuously increase as the retention interval increases.

    “However, such research also emphasizes that the effect of retention intervals on the distributed practice advantage does not continuously increase as the retention interval increases (Cepeda et al., 2008).”

    From The Distributed Practice Effect on Classroom Learning: A Meta-Analytic Review of Applied Research (2025) · cites this paper as Cepeda et al., 2008

    The Discussion (page unavailable) reports that the optimal study gap increases as the retention interval increases, while the ratio of optimal gap to retention interval declines. It also describes a non-monotonic effect of the study gap at a given retention interval. These findings show that spacing effects depend on retention interval, but they do not establish the claimed non-monotonic change in the distributed-practice advantage as retention intervals increase. (LLM, conf=0.78)

    Experimental — accuracy not yet measured

  • Learning is not spaced-out in written assessments despite evidence that enduring retention is achieved through substantial gaps in practice.

    “There are two issues: (1) learning is not spaced-out despite evidence that enduring retention is achieved through substantial gaps in practice (gaps of months to achieve knowledge lasting years) (Cepeda et al., 2008);”

    From Using version control to document genuine effort in written assignments: a protocol with examples for universities (2023) · cites this paper as Cepeda et al., 2008

    The Educational Implications section says that studying a topic within a single course week is at odds with the evidence, and that a review delayed by several months is likely to aid retention over several years. It supports the point about insufficient spacing in conventional education, but does not specifically establish that learning is not spaced out in written assessments. (LLM, conf=0.84)

    Experimental — accuracy not yet measured

  • The optimal spacing depends on the retention interval.

    “According to cognitive psychologists (Cepeda et al., 2008;Rohrer & Pashler, 2007), the optimal spacing depends on the retention interval (i.e., the timing of delayed posttest).”

    From MASSED TASK REPETITION IS A DOUBLE-EDGED SWORD FOR FLUENCY DEVELOPMENT (2022) · cites this paper as Cepeda et al., 2008

Cites

Flagged first, then by citations

Research works printed but not linked: 2

  1. Murray J.T., 1983, Dissertation Abstracts International, 43, 3058
  2. Young J.L., 1966, Dissertation Abstracts International, 27, 3699

Cited by

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Related

Authors
Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H.
Affiliations
  • York University (CA)
  • University of California San Diego (US)
  • University of South Florida (US)
Corresponding author
Pashler, Harold
ORCID
Venue
Psychological Science
Publisher
SAGE Publications
Published
2008-11
Volume
19
Issue
11
Pages
1095-1102
ISSN
  • 0956-7976 (ISSN-L)
  • 1467-9280
DOI
10.1111/j.1467-9280.2008.02209.x
OpenAlex
W2169419728
Cited by
631
References
32
Citations by year
2026: 41 · 2025: 54 · 2024: 52 · 2023: 39 · 2022: 51 · 2021: 54 · 2020: 38 · 2019: 49 · 2018: 36 · 2017: 27 · 2016: 25 · 2015: 31 · 2014: 34 · 2013: 25 · 2012: 44
FWCI
5.17
Type
journal article
Language
en
Open access
Licence
journals.sagepub.com/page/policies/text-and-data-mining-license (tdm)
Locations
  • Psychological Science (publishedVersion)
  • PubMed (publishedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
  • Digital Commons - University of South Florida (University of South Florida) (submittedVersion)
Funders
  • National Science Foundation (0542013, 0720375)
  • U.S. Department of Education
  • Institute of Education Sciences
Topics
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Memory Processes and Influences
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Visual and Cognitive Learning Processes
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Memory and Neural Mechanisms
Keywords
spacing effect, retention, test delay, spaced learning, long-term memory
MeSH terms
Adolescent, Adult, Aged, Female, Humans, Learning, Male, Memory, Middle Aged, Retention, Psychology, Space Perception, Time Factors, Young Adult

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